You are creating what is known as a hash of arrays (HoA), rather than a two-dimensional hash (HoH). To print the array, I would write this:

my %link;
push @{ $link{testing} }, "fred";
push @{ $link{testing} }, "stan";
print join " ", @{ $link{testing} }, "\n";
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You print statement did not work because you needed to dereference the array reference $link{testing}.